One way to help understand Ravnica lore is understanding the foundation in mana. In the MtG card game that the setting is based on, all Ravnican guilds are aligned with two of the five colours of magic; White, Blue, Black, Red, Green. For example Boros Legion is White/Red.
Each colour represents a mix of positive, neutral, and negative traits. Some of these traits are:
- White: Law, loyalty, discipline, tyranny, oppression, authoritarianism
- Blue: Knowledge, discovery, secrets, subterfuge, control, manipulation
- Black: Determination, autonomy, drive, selfishness, cruelty
- Red: Passion, love, freedom, destruction, anarchy, chaos
- Green: Growth, rebirth, life, death, decay
The colours are arranged in a wheel: White > Blue > Black > Red > Green > back to White. This wheel expresses two core concepts of each colour; it's allies (the two colours adjacent to it) and it's enemies (the two colours opposite it)
For example, Red is allied with green and black, but enemies with white and blue
This applies to Ravnica because it lets you understand how the guilds relate; Boros Legion is a military organisation aligned with white and red mana. This gives you not only an idea of their disposition (passionate yet disciplined, orderly yet aggressive), but also how they interact with the other guilds. For example, they share white mana alignment with the Orhzov Syndicate (white/black), the Azorius Senate (white/blue), and the Selesnya Conclave (white/green). They share their red mana alignment with the Cult of Rakdos (black/red), Izzet League (blue/red), and Gruul Clans (red/green). This allows you to understand that a Boros Legion individual would likely have some relation or in-road with one of those guilds in some capacity
However, the Boros Legion shares no colour alignment with the Simic Combine (blue/green), Golgari Swarm (black/green), or House Dimir (blue/black)